There are a number of conventional processes for packaging integrated circuit (IC) dice. By way of example, many IC packages utilize a metallic leadframe. The leadframe typically includes a plurality of leads or contacts, and optionally a die attach pad (paddle) upon which a die may be physically attached by means of a suitable adhesive material. The die is typically electrically connected to the leadframe leads by means of bonding wires. In general, the die and portions of the leadframe are encapsulated with a molding material to protect the electrical connections and the delicate electrical components on the active side of the die.
During the encapsulation process, the die, leadframe and other components may be subjected to temperatures reaching and or even exceeding 175° C. before being cooled to room temperature (25° C.). With rapid exposure to such a high temperature, moisture located within the device expands rapidly. Of particular concern is any moisture located in the interface between a die and die attach material and between the die attach material and a die attach pad. In addition to the rapid expansion of moisture, non-uniform expansion as a result of the differences in the coefficients of thermal expansion of the die, die attach material, leadframe and molding material leads to high stresses that can result in delamination, or separation, of the die from its associated die attach pad or paddle (DAP). Additionally, the expansion may result in damaged wire bonds, internal cracks and/or other damage to the die itself. Generally, the risk of delamination or other damage is amplified with decreased heating and cooling times. That is, the faster the device is heated and cooled, the greater the induced stresses and the greater the risk of delamination and other damage.
Other high stress inducing processes include solder reflow and mounting. Additionally, it should be appreciated that thermal variations due to standard device operation induce stresses and that these stresses may also lead to device damage. More particularly, the repetitive powering on and off during standard device operation leads to cyclic stresses that, over extended periods of time, may result in significant damage to the device, such as delamination, and even render the device inoperable.
Hence, there are continuing efforts to reduce stresses and to provide structures that reduce the probability of die delamination and other damage in IC packages.